1. Field of the Invention
This invention relates to extruded sheets and, more particularly, to an apparatus for continuously forming a sheet product using a roll stand assembly with cooperating rolls defining a nip location at which flowable material is continuously delivered from a sheet die during the sheet product formation process.
2. Background Art
Extruded sheets are formed from many different materials, with many different thicknesses, and with different layer constructions. An extruded sheet may be formed by itself or combined with one or more other sheet layers that are concurrently formed, or combined after formation.
In a typical apparatus for extrusion forming sheet products, a roll stand assembly is placed downstream of an extruder assembly with an associated sheet die. Flowable material is delivered to the sheet die to a nip/lamination location between adjacent rolls on the roll stand assembly. The applied material is advanced through a gap between the adjacent rolls defined at the nip location from where it may be routed between one or more additional roll pairs before it arrives at a downstream accumulation location at which a final sheet product may be rolled, stacked, packaged, staged, or otherwise handled or processed.
In this type of apparatus, the relative vertical positions of the sheet die and nip location are varied, dependent upon the nature of the flowable material and the thickness applied at the nip location. This relationship is typically controlled by changing the height of the upstream end of the roll stand assembly. Heretofore, the vertical movement of the end of the roll stand assembly has been effected either manually or through mechanisms that are power driven.
Manual repositioning of the upstream end of the roll stand assembly is typically carried out by changing the relationship between laterally spaced supporting casters and a main frame on the roll stand assembly. A plurality of such casters is incorporated to guide movement of the roll stand assembly in a horizontal path selectively towards and away from the sheet die. The mounting mechanisms for the casters at the upstream end of the roll stand assembly are designed to be reconfigured through manual turning of one or more threaded components to selectively raise and lower the upstream end of the roll stand assembly.
The manual systems have a number of drawbacks. First of all, a separate tool is required to be kept on hand to make the necessary adjustments. This is an inconvenience in itself. In the event that the required tools are not immediately on hand, there may be delays experienced in effecting the necessary adjustments.
Components that are operated with conventional tools, such as wrenches and screwdrivers, are prone to being worn and stripped. This problem is aggravated by providing the adjusting elements within protective housings where they are not exposed for ready access, as a result of which the tools may not be properly aligned as the requisite movement of the adjusting elements is effected/attempted.
Such adjusting elements are relatively small and typically made from metal that is prone to becoming compromised by rust and corrosion caused by exposure to moisture and/or chemicals present in the working environment. This could cause these elements to seize, which may necessitate corrective actions that are time consuming and inconvenient.
Further, the roll stand assemblies are generally heavy components. To effect elevation of the upstream end of the roll stand assembly, a force imparted to the mechanism associated with the caster is resisted by the substantial weight of the roll stand assembly. This could also lead to stripping of the adjusting elements.
A still further problem with mechanical systems is that they are separately provided at each lateral side of a main frame on the roll stand assembly. An operator is therefore required to move from one side to the other to assure that the upstream end of the roll stand is level and elevated, or lowered, to the appropriate height. If gross changes are made on one side of the main frame, the entire roll stand assembly may skew. This condition may not be completely remedied, as a result of which the roll stand assembly may not be properly aligned with the other system components, and particularly the sheet die. This may lead to a compromise in the sheet product that is formed using the roll stand assembly.
Still further, operators have been required to either manually measure or eye the vertical relationship between the sheet die and nip location during this process. This is inherently inconvenient and may lead to imprecise vertical adjustment between the nip location and sheet die. This also adds significantly to the set-up time for the system as the user progressively moves the upstream end of the roll stand assembly in a vertical direction and attempts to achieve a precise relationship and maintain full level between the sides of the main frame.
Powered systems overcome some of the above problems but introduce others. Powered systems are inherently expensive, particularly given the heavy nature of this type of equipment.
Additionally, powered systems are relatively complex in nature and prone to failure. In the event that the vertical repositioning structure is for some reason not operating as required, the entire system into which the roll stand assembly is incorporated may be down while repairs are made. This can have a significant financial impact.
While the above apparatus have a number of drawbacks, the industry has continued to use them because it was lacking any substitute structure that addresses all of the issues relating to cost, convenience, reliability, and accuracy.